(1) Field of the Invention
This invention relates to electroplated extremely high corrosion resistant steels and a method for producing same.
(2) Description of the Prior Art
The Zn-plating or galvanizing is widely resorted to in the art as means for imparting corrosion resistance to the surfaces of steel materials. In this connection, it is known that electrogalvanized steel plates are generally inferior to dip-plated steel plates in corrosion resistance due to the difficulty of forming zinc coatings of sufficient thickness by the electrogalvanizing process. Therefore, there have heretofore been made various attempts without increasing the metal deposition of the electrogalvanized steel plates to guarantee a higher corrosion resistance (e.g., Japanese Laid-Open Patent Specification No. 53-89835).
In the meantime, the present inventors developed a steel material with surfaces of high corrosion resistance, having an intermediate plated layer of a Zn-Ni alloy and an outer electrogalvanized layer on a base steel plate (Japanese Patent Application No. 54-113725, Kobe Steel Technical Report vol. 30, No. 1, pp. 64-67).